Question
A 5-year-old boy presented to paediatric OP with fever, sore throat, difficulty in swallowing. He has no records of vaccination O/E cervical lymphadenopathy and white patch seen on the tonsil. (
- (a) What is your clinical diagnosis. ( 1 mark(s)
- (b) Name the causative organism. ( 1 mark(s)
- (c) Describe the pathogenesis of this condition. ( 3 mark(s)
- (d) How do you confirm the diagnosis in the laboratory. (e) How do you manage the child. (f) What are the public health measures you have to take to prevent the spread of infection. 4 mark(s)
Answer
(a) Clinical diagnosis: Diphtheria — an unvaccinated child with fever, sore throat, cervical lymphadenopathy, and a white patch (pseudomembrane) on the tonsil is the classical presentation.
(b) Causative organism: Corynebacterium diphtheriae (toxigenic strains).
(c) Pathogenesis: C. diphtheriae colonizes the pharyngeal mucosa (non-invasive) and, if lysogenized by a bacteriophage carrying the tox gene, produces diphtheria exotoxin. Locally, the toxin causes epithelial necrosis and an intense inflammatory exudate composed of fibrin, dead cells, and bacteria, forming the characteristic tough, greyish-white pseudomembrane that bleeds if forcibly removed, and can extend to obstruct the airway. The toxin is absorbed systemically and, via ADP-ribosylation of elongation factor-2, inhibits host cell protein synthesis in distant organs, causing toxic myocarditis and peripheral/cranial neuropathy — the major life-threatening complications of the disease.
(d) Laboratory confirmation:
- Direct microscopy — Gram stain and Albert’s/Neisser’s stain of a throat/pseudomembrane swab, showing club-shaped, Gram-positive bacilli arranged in characteristic Chinese-letter/V, L patterns, with metachromatic (volutin) granules on Albert’s stain.
- Culture — on Loeffler’s serum slope (for rapid growth and morphology) and Tellurite blood agar (selective medium, producing characteristic black/grey colonies).
- Toxigenicity testing — Elek’s gel precipitation test (in-vitro toxin-antitoxin precipitation test), or PCR detection of the tox gene, to confirm that the isolate is toxin-producing (essential, since only toxigenic strains cause the systemic disease).
(e) Management: Diphtheria Antitoxin (DAT), administered promptly (ideally after a test dose to screen for hypersensitivity) to neutralize circulating unbound toxin — antitoxin does not reverse toxin already bound to tissue, so early administration is critical; combined with antibiotic therapy (Penicillin or Erythromycin) to eradicate the organism and halt further toxin production; supportive care including airway monitoring/management (given risk of airway obstruction) and cardiac monitoring (for myocarditis); strict bed rest to minimize cardiac strain.
(f) Public health measures:
- Isolation of the patient (droplet precautions) until proven non-infectious (e.g., two negative throat cultures).
- Contact tracing — identification and surveillance of close contacts, with antibiotic prophylaxis (e.g., Erythromycin) for close contacts regardless of immunization status, and booster vaccination for incompletely immunized contacts.
- Case notification to public health authorities, given diphtheria’s status as a notifiable disease.
- Strengthening routine immunization coverage in the community — this case, occurring in an unvaccinated child, underscores the importance of ensuring high DPT vaccine coverage to maintain herd immunity and prevent resurgence.